Move checking an explicit VARIADIC "any" argument into the parser.

This is more efficient and simpler . It does mean that an untyped NULL
can no longer be used in such cases, which should be mentioned in
Release Notes, but doesn't seem a terrible loss. The workaround is to
cast the NULL to some array type.

Pavel Stehule, reviewed by Jeevan Chalke.

src/include/parser/parse_func.h

@@ -52,8 +52,8 @@ extern FuncDetailCode func_get_detail(List *funcname,
 				int nargs, Oid *argtypes,
 				bool expand_variadic, bool expand_defaults,
 				Oid *funcid, Oid *rettype,
-				bool *retset, int *nvargs, Oid **true_typeids,
-				List **argdefaults);
+				bool *retset, int *nvargs, Oid *vatype,
+				Oid **true_typeids, List **argdefaults);
 
 extern int func_match_argtypes(int nargs,
 					Oid *input_typeids,